Maui’s Honolua Bay is a water worshipper's holy place, drawing snorkelers and scuba divers in the warmer months, and surfers waiting for a life-changing swell when winter comes. But look carefully. Beyond the spot’s wild beauty, you’ll notice something else: a sheen of sunscreen coating the water’s surface.

It’s an ominous reminder of the 14,000 tons of sunblock bleeding into the global coral reef system every year. And there’s damage beneath the surface: Research shows that ingredients in some forms of popular sunblock, one called oxybenzone in particular, can lead to fatal coral reef bleaching. Some studies suggest one drop is enough to do damage.

To understand the issue at hand, though, you have to first understand a bit about sunscreen in general—and how it has an impact on marine life.

Sunscreen 101

Sunblock comes in two forms: chemical and physical blockers. Chemical sunscreens work like chemical sponges, says Melissa Levin, M.D., a dermatologist at Marmur Medical in New York City. They convert and neutralize ultraviolet light radiation, protecting you from damage, she says. Physical blockers, on the other hand, act like a shield. “They sit on the skin’s surface and actually reflect the sun’s rays like a mirror would reflect light.”

When it comes to the environment, the chemical ones are the problem. (Take Hawaii State Department’s signs that read: ‘If You Can’t Say It, Don’t Spray It.’) In Honolua Bay alone, some reports suggest oxybenzone exists at nearly 2,000 parts per trillion. Other research, led by Craig Downs, Ph.D., who studies the topic and is the executive director of Haereticus Environmental Laboratory, finds that oxybenzone levels exceed 700 parts per trillion early in the morning on Hawaii beaches—before swimmers even show up. To put that in perspective: He says damage can occur at concentrations as low as 62 parts per trillion.

Surfers Are 'Canaries in the Coal Mines'

Outside of Hawaii's efforts to ban the sales of harmful sunscreens across the islands, those who love the ocean—and the places hurt the most by damage—are leading some of the efforts toward change.

“We love to surf in clean and beautiful waters,” says Cyrus Sutton, a film director, professional surfer, and founder of Manda Naturals, a ‘reef-friendly’ sun paste he started after almost losing his father to skin cancer. “For a long time, there has been a disconnect in our own habits.”

But that’s changing. Surfboards are eco-friendly. Ingredient-conscious sun pastes line the walls of surf shops. People are starting to pay attention. Manda, which uses ingredients like coconut oil, beeswax, and zinc powder to block the sun’s damage rays, while also protecting the reefs, was born out of that want for something healthier.

“I have been surfing professionally since I was 18, and I really took my health into own hands,” says Sutton. “I wanted anything that went on my body to be as natural as possible—and that extended to my sunblock. ... Surfers are really looking at their impact on the places they love the most. We are canaries in the coal mines, to some extent.”

How to Have an Impact

Ingredients like oxybenzone don’t just harm coral reefs. Referred to as an "endocrine disruptor," the ingredient can affect fish in the Great Lakes, kelp beds, shrimp, lobster, sea urchins, and dolphins; there's even research that sunscreen chemicals can be transferred via breast milk, says Downs. It’s not just Hawaii that’s at risk, either. “Wherever there are resorts and tourists, those coral reefs are potentially going to be threatened by the use of sunscreen,” he says.

Remote areas are not immune to damage, either. Downs’s team has found oxybenzone everywhere from five miles off the coast of Key Largo to secluded areas in the Pacific islands.

Of course, no product is perfect. Downs notes that even some forms of titanium dioxide and zinc oxide, both commonly found in sunscreens, can have a toxic effect on the sea. Many newer "reef safe" blocks still need to go through extensive testing, he notes. But experts agree that physical sunscreens are a big step up—a safer bet for both your skin (physical blockers are less likely cause irritation, says Levin) and the environment.

For a place to start, check out these skin-friendly, environmentally friendly brands: